Upload
cale
View
29
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Evaluation of the ground retracking algorithms on Jason-1 data. P.Thibaut, S. Labroue Collecte Localisation Satellite : Toulouse, France. All the results presented have been obtained on one cycle of Jason-1 data (cycle 20). GDR ‘B’ nominal Jason-1 products - PowerPoint PPT Presentation
Citation preview
Evaluation of the ground retracking algorithms on
Jason-1 data P.Thibaut, S. LabroueCollecte Localisation Satellite : Toulouse,
France
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 2
Objective
The objective of this presentation is to characterize the various retracking
algorithms applied on Jason and Topex waveforms and to determine if they can be
considered as responsible for differences observed between Jason and Topex
SSB.
We decided to apply the various retracking on Jason-1 WFs. If no differences
are observed when retracking the same waveforms, the differences between
Topex and Jason SSB may directly come from the WFs (leakages on Topex WFs) All the results presented have been obtained on one cycle of Jason-1 data (cycle 20)
• GDR ‘B’ nominal Jason-1 products• Retracked files provided by JLP (same information than in Topex RGDRs including LSE and MAP estimations)
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 3
Characteristics of the 3 retracking algorithms
MLE4(nominal proc.for GDRs) :
LSE
MAP
• Epoch, SWH, Pu, slope of the trailing edge : 20 estimations per second• Retracking a single gaussian + LUT which provide the correction between one gaussian and the full real PTR (as a function of SWH)• Skewness s set to 0.1
• Waveforms averaging (2x2 in Ku band, 4x4 in C band) before retracking• Decomposition of the PTR into a sum of Gaussians (for 20 side-lobes)• Epoch : 10 estimations per second in Ku (5 in C)• SWH, Pu, slope of the trailing edge : 1 estimation per second• s : 1 estimation per second or fixed to 0
• Idem LSE
Allows comparisonto Topex LSE
Allows comparisonto Jason MLE4
(except that for Jason a 0.1 value is used)
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 4
Range1Hz = TrackerGDR – EpochJPL – LUTGDR – RangeGDR_1Hz
Information provided by the various products
JPL products provide:the retracked epoch (10 Hz and 1 Hz) (JPL = LSE or MAP) : EpochJPL
GDR products provide:the range (20 Hz and 1Hz) : RangeGDR
the tracker range (20Hz and 1 Hz) : TrackerGDR
the Look Up Table correction for epoch (1Hz) : LUTGDR
Comparison between JPL and GDR ranges is given by:
Range1Hz = RangeJPL_1Hz – RangeGDR_1Hz
But we have only the EpochJPL
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 5
Delta Range(LSE - GDR) versus (SWH and SIG0)
40 cm 50 cm
No remaining dependancies with SWH or SIG0 in the bulk of the data
Skewness solved Range_LSE-Range_GDR versus (SWH,SIG0)
Skew solved
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 6
Delta Range(LSE - GDR) versus (SWH and ATT2)
40 cm 50 cm
No remaining dependancies with SWH or ATT2 in the bulk of the data
Range_LSE-Range_GDR versus (SWH,ATT)
Skew solved
Skewness solved
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 7
Delta Range(LSE - GDR) versus (SWH and SIG0 and ATT2)
Dependances appear when the skewness is fixed but it was fixed to 0 (in GDR 0.1)
Range_LSE-Range_GDR versus (SWH,ATT)
Skew fixed
Range_LSE-Range_GDR versus (SWH,SIG0)
Skew fixed
40 cm 50 cm 40 cm 50 cm
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 8
SWH
LSE-GDR
MAP-GDR
SWH
ATT2
ATT2
Range
Range
Very good agreement between LSE and MLE4
MAP introduces SWH and ATT dependances
(Constraints on MAP skewness is too strong : s=0)
Skewness solved
45 cm
50 cm
45 cm
50 cm
1%SWH
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 9
Delta Range(MAP - GDR) versus (SWH and SIG0 and ATT2)
MAP introduces dependances but the skewness remains close to 0 (in GDR 0.1) Same kind of plot when skewness fixed at 0
Range_MAP-Range_GDR versus (SWH,ATT) Skew solved
Range_MAP-Range_GDR versus (SWH,SIG0) Skew solved
40 cm 50 cm 40 cm 50 cm
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 10
Difference of range (LSE – MAP)
-5cm +5cm
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 11
Skewness estimation
LSE MAP
Skewness is not estimated for SWH smaller than 1 m Skewness remains close to 0 for MAP
Mean=0.06 Mean=0.001
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 12
Skewness with respect to SWH
LSE MAP
Skewness is not estimated for SWH less than 1 m Skewness remains close to 0 for MAP
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 13
ATT_LSE ATT_MAPATT_GDR
ATT(LSE-GDR) ATT(MAP-GDR)
Statistics on ATT – Skewness Solved
Mean=-0.002 Mean=-0.003
Mean=0.003 Mean=0.001 Mean=0.001
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 14
Statistics on SWH
SWH(LSE-GDR) SWH(MAP-GDR)
Skewnesssolved
Skewnessfixed
Mean=7.64 cm Mean=7.91 cm
Mean=28.8 cmMean=7.06 cm
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 15
Jason-1 SLA Power Spectrum
J1 LSE5
TP LSE5
J1 MLE4 (GDRB)
J1 LSE4 (fixed skew)
Very good coherence between Topex LSE5 and Jason MLE4 Between MLE4 and LSE4, impact of 1HZ estimation for SWH, Pu and Att2 (skew fixed for both) Between LSE4 and LSE5, impact of the estimation of a 5th parameter (s) Between MLE4 and LSE5, addition of the two previous effects (it has been shown that they are very close regarding the SSB)
(see Faugere’s talk)
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 16
Conclusions
• LSE and MLE4 algorithms are equivalent wrt SSB when skewness is solved for.
• SSB differences between Topex and Jason cannot be explained by differences in the retracking algorithms
• SSB differences lie in the WFs themselves • SWH biases (LSE) are still to be analysed • MAP is not yet ready to provide users with reliable estimates
Range_LSE-Range_GDR versus (SWH,SIG0)
Skew solved
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 17
Simulator of Interferometric Radar Altimeters
concept and first resultsP. THIBAUT, B.PICARD : CLS, France, O.GERMAIN : Starlab, Spain, F.COLLARD : Boost-Technologies, France
L.PHALIPPOU : Alcatel-Alenia-Space, France C.BUCK5 : ESTEC-ESA, The Netherlands
PRF-1
Vsat
Left swathRight swath
Nadir track
Sea State Modelling
Waveform generation
Boost
Starlab
InterferometricInversion
CLS
CLS
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 19
Hobart OSTST MeetingPierre THIBAUT – March 2007 Page 20
Sigma-0 blooms in the Envisat Radar Altimeter dataP.THIBAUT, F.FERREIRA : CLS, France, P.FEMENIAS :
ESA/ESRIN, Italy
Which one is a bloom, which one is not ?Where are the egdes ?What are their length ? Where are they ?What about the waveforms during blooms ?What are the impact of blooms on ranges ?How many blooms are edited by Calval criteria?Which kind of criteria would be more useful ? ….Ideas, comments …. Come to talk with me.